25.04.2011
Microelectronics
Circuit Analysis and Design
Donald A. Neamen
Chapter 7
Frequency Response
Neamen
Microelectronics, 4e
McGraw-Hill
Chapter 7-1
In this chapter, we will:
 Discuss the general frequency response
characteristics of amplifiers.
 Derive the system transfer functions
 Develop the Bode diagrams of the magnitude
and phase of the transfer functions.
 Analyze the frequency response of transistor
circuits with capacitors.
 Determine the Miller effect and Miller
capacitance
capacitance.
 Determine the high-frequency response of basic
transistor circuit configurations.
Neamen
Microelectronics, 4e
McGraw-Hill
Chapter 7-2
1
25.04.2011
Amplifier Gain Versus Frequency
Neamen
Microelectronics, 4e
McGraw-Hill
Chapter 7-3
Transfer Functions of
the Complex Frequency
Name of Function
Expression
p
Voltage Transfer Function
T(s) = Vo(s)/Vi(s)
Current Transfer Function
Io(s)/Ii(s)
Transresistance Function
Vo(s)/Ii(s)
Transconductance Function
Io(s)/Vi(s)
Neamen
Microelectronics, 4e
McGraw-Hill
Chapter 7-4
2
25.04.2011
Series Coupling Capacitor Circuit
s
)
1  s
  ( RS  RP )C S
T ( s)  K 2 (
Neamen
Microelectronics, 4e
McGraw-Hill
Chapter 7-5
Parallel Load Capacitor Circuit
1
)
1  s
  ( RS RP )C P
T ( s )  K1 (
Neamen
Microelectronics, 4e
McGraw-Hill
Chapter 7-6
3
25.04.2011
Bode Plot of Voltage Transfer Function
Magnitude:
Series Coupling Capacitor Circuit
Neamen
Microelectronics, 4e
McGraw-Hill
Chapter 7-7
Relationship Between Rectangular
and Polar Coordinates
Neamen
Microelectronics, 4e
McGraw-Hill
Chapter 7-8
4
25.04.2011
Bode Plot of Voltage Transfer Function
Phase:
Series Coupling Capacitor Circuit
Neamen
Microelectronics, 4e
McGraw-Hill
Chapter 7-9
Bode Plot of Voltage Transfer Function
Magnitude:
Parallel Load Capacitor Circuit
Neamen
Microelectronics, 4e
McGraw-Hill
Chapter 7-10
5
25.04.2011
Bode Plot of Voltage Transfer Function
Phase:
Parallel Load Capacitor Circuit
Neamen
Microelectronics, 4e
McGraw-Hill
Chapter 7-11
Circuit with Series Coupling and
Parallel Load Capacitor
 S  ( RS  RP )C S
 P  ( RS RP )C P
fL 
fH 
Neamen
Microelectronics, 4e
McGraw-Hill
1
2 S
1
2 P
Chapter 7-12
6
25.04.2011
Bode Plot of Magnitude of Voltage
Transfer Function:
Series Coupling and Parallel Load Capacitor
Neamen
Microelectronics, 4e
McGraw-Hill
Chapter 7-13
Steady-State Output Response
Coupling Capacitor
Neamen
Microelectronics, 4e
McGraw-Hill
Load Capacitor
Chapter 7-14
7
25.04.2011
Common Emitter with Coupling
Capacitor
fL 
Neamen
1
2 ( RSi  Ri )CC
Microelectronics, 4e
McGraw-Hill
Chapter 7-15
Common Source with Output
Coupling Capacitor
fL 
Neamen
Microelectronics, 4e
McGraw-Hill
1
2 ( RD  RC )CC
Chapter 7-16
8
25.04.2011
Emitter Follower with Output
Coupling Capacitor
fL 
Neamen
Microelectronics, 4e
McGraw-Hill
1
2 ( Ro  RL )CC 2
Chapter 7-17
Problem-Solving Technique:
Bode Plot of Gain Magnitude
1 Determine whether capacitor is producing a
1.
low-pass or high-pass circuit.
a. Sketch general shape of Bode plot
2. Corner frequency is f = 1/(2) where  = ReqC
a. Req is resistance seen by capacitor
3. Maximum gain magnitude is midband gain.
a. Coupling and bypass capacitors act as
shorts
b. Load capacitors act as opens
Neamen
Microelectronics, 4e
McGraw-Hill
Chapter 7-18
9
25.04.2011
Common Source with Load Capacitor
fH 
Neamen
Microelectronics, 4e
McGraw-Hill
1
2 ( Ro RL )CL
Chapter 7-19
Coupling and Parallel Load Capacitors
Neamen
Microelectronics, 4e
McGraw-Hill
Chapter 7-20
10
25.04.2011
Small-Signal Equivalent Circuit:
Coupling and Parallel Load Capacitor
fL 
1
2 [ RS  ( R1 R2 Ri )]CC
Neamen
Microelectronics, 4e
McGraw-Hill
fH 
1
2 ( RC RL )C P
Chapter 7-21
Emitter Bypass Capacitor
Neamen
Microelectronics, 4e
McGraw-Hill
Chapter 7-22
11
25.04.2011
Bode Plot of Voltage Gain Magnitude:
Emitter Bypass Capacitor
Neamen
Microelectronics, 4e
McGraw-Hill
A v  0 
g m r RC
RS  r  (1   ) RE
A v   
g m r RC
RS  r
Chapter 7-23
Two Coupling Capacitors and a
Emitter Bypass Capacitor
Neamen
Microelectronics, 4e
McGraw-Hill
Chapter 7-24
12
25.04.2011
PSpice Results for Two Coupling
Capacitors and a Emitter Bypass
Capacitor
Neamen
Microelectronics, 4e
McGraw-Hill
Chapter 7-25
Expanded Hybrid  Equivalent Circuit
Neamen
Microelectronics, 4e
McGraw-Hill
Chapter 7-26
13
25.04.2011
Short-Circuit Current Gain:
Analysis of Frequency Response of BJT
Neamen
Microelectronics, 4e
McGraw-Hill
Chapter 7-27
Bode Plot:
Short-Circuit Current Gain
f 
Neamen
1
2 r (C  C )
Microelectronics, 4e
McGraw-Hill
fT   o f 
Chapter 7-28
14
25.04.2011
2-Port Equivalent Circuit of CBJT
Thevenin Equivalent
Neamen
Norton Equivalent
Microelectronics, 4e
McGraw-Hill
Chapter 7-29
Small-Signal Equivalent Circuit with
Miller Capacitance: BJT
CM  C [1  g m ( RC RL )]
Neamen
Microelectronics, 4e
McGraw-Hill
Chapter 7-30
15
25.04.2011
Inherent Resistances and
Capacitances in n-Channel MOSFET
1
C gs  C gd  WLC ox
2
Neamen
Microelectronics, 4e
McGraw-Hill
Chapter 7-31
Equivalent Circuit for n-Channel
Common Source MOSFET
Neamen
Microelectronics, 4e
McGraw-Hill
Chapter 7-32
16
25.04.2011
Unity-Gain Bandwidth
fT 
Neamen
gm
2 (C gs  C gd )
Microelectronics, 4e
McGraw-Hill
Chapter 7-33
Small-Signal Equivalent Circuit with
Miller Capacitance: MOSFET
C M  C gd [1  g m RL ]
Neamen
Microelectronics, 4e
McGraw-Hill
Chapter 7-34
17
25.04.2011
Common-Emitter Amplifier
Neamen
Microelectronics, 4e
McGraw-Hill
Chapter 7-35
High-Frequency Equivalent Circuit:
Common Emitter
fH 
Neamen
1
2 [r RB RS ](C  C  )
Microelectronics, 4e
McGraw-Hill
Chapter 7-36
18
25.04.2011
PSpice Results for Common Emitter
Neamen
Microelectronics, 4e
McGraw-Hill
Chapter 7-37
Common-Base Amplifier
Neamen
Microelectronics, 4e
McGraw-Hill
Chapter 7-38
19
25.04.2011
High-Frequency Equivalent Circuit:
Common Base
f H 
1
f H 
r
2 [  RB RS ]C
1 
Neamen
Microelectronics, 4e
McGraw-Hill
1
2 ( RC RL )C 
Chapter 7-39
PSpice Results for Common Emitter
Neamen
Microelectronics, 4e
McGraw-Hill
Chapter 7-40
20
25.04.2011
Cascode
Circuit
Neamen
Microelectronics, 4e
McGraw-Hill
Chapter 7-41
High-Frequency Equivalent Circuit:
Cascode
f H 
1
2 [ RS RB1 r 1 ](C 1  C M 1 )
Neamen
Microelectronics, 4e
McGraw-Hill
f H 
1
2 ( RC RL )C  2
Chapter 7-42
21
25.04.2011
PSpice Results for Cascode
Neamen
Microelectronics, 4e
McGraw-Hill
Chapter 7-43
Emitter-Follower Circuit
Neamen
Microelectronics, 4e
McGraw-Hill
Chapter 7-44
22
25.04.2011
High-Frequency Equivalent Circuit:
Emitter Follower
fH 
1
2 [ RS RB (1  g m RL' )r ](C  
Neamen
C
)
1  g m RL'
Microelectronics, 4e
McGraw-Hill
Chapter 7-45
PSpice Results for Emitter Follower
Neamen
Microelectronics, 4e
McGraw-Hill
Chapter 7-46
23